Aluminum Nitride Synthesis from Nut Shells

ABSTRACT

Nano-structures of Aluminum Nitride and a method of producing nano-structures of Aluminum Nitride from nut shells comprising milling agricultural nuts into a fine nut powder, milling nanocrystalline Al2O3 into a powder, mixing, pressing the fine nut powder and the powder of nanocrystalline Al2O3, heating the pellet, maintaining the temperature of the pellet at about 1400° C., cooling the pellet, eliminating the residual carbon, and forming nano-structures of AlN. An Aluminum Nitride (AlN) product made from the steps of preparing powders of agricultural nuts using ball milling, preparing powders of nanocrystalline Al2O3, mixing the powders of agricultural nuts and the powders of nanocrystalline Al2O3 forming a homogenous sample powder of agricultural nuts and Al2O3, pressurizing, pyrolyzing the disk, and reacting the disk and the nitrogen atmosphere and forming AlN.

REFERENCE TO RELATED APPLICATION

This application is a non-provisional of, and claims priority to and thebenefits of, U.S. Patent Application Ser. No. 62/422,793 filed on Nov.16, 2016 and U.S. patent application Ser. No. 15/786,180 filed on Oct.17, 2017 and U.S. patent application Ser. No. 16/406,969 filed on May 8,2019, the entirety of each is hereby incorporated by reference.

BACKGROUND

This invention concerns a new method for the formation of abundantquantities of Aluminum Nitride (AlN) from a thermal treatment of amixture of aluminum oxide (Al₂O₃) and shells of almond, cashew,coconuts, pistachio, and walnuts in a nitrogen atmosphere attemperatures in excess of 1450° C.

This new method of synthesizing Aluminum Nitride from various Nut Shellsuses conventional heating or microwave heating to producenano-structures.

Billions of pounds of agricultural waste of nut shells such as those ofalmonds, pistachios, walnuts, cashew, coconuts, macadamia etc. aregenerated every year all over the world.

Aluminum Nitride (AlN) is a very useful material for industrial andelectronic applications due to its unique physical properties.

AlN is an insulator in electronic device applications because of highelectrical resistivity, low thermal expansion, resistance to erosion andcorrosion, excellent thermal shock resistance and chemical stability inair up to 1380° C. with surface oxidation occurring at 780° C.

Surface acoustic wave sensors (SAWs) can be deposited on silicon wafersbecause of AlN's piezoelectric properties and AlN can be used as an RFfilter for mobile phones.

AlN is synthesized in the bulk form by the carbothermal reduction ofaluminum oxide in the presence of gaseous nitrogen or ammonia or bydirect nitridation of aluminum. In order to get a fully dense form, Y₂O₃or CaO are required as additives during the hot pressing.

Aluminum nitride is a wide gap semiconductor with band gap between6.01-6.05 eV at room temperature. It crystallizes in wurtzite phase andhas many potential applications in microelectronics due to itsrelatively high thermal conductivity (70-210 W·m⁻¹·K⁻¹ to 285W·m⁻¹·K⁻¹). In addition, other unique properties that make it anattractive for applications include high electrical resistivity, lowthermal expansion, resistance to erosion and corrosion, excellentthermal shock resistance and chemical stability in air up to 1380° C.with surface oxidation occurring at 780° C.

Epitaxially grown thin film crystalline aluminum nitride is used forsurface acoustic wave sensors (SAWs) deposited on silicon wafers becauseof AlN's piezoelectric properties. Another important application for AlNis its application as an RF filter which is widely used in mobilephones, which is also called a thin film bulk acoustic resonator (FBAR).AlN is synthesized in the bulk form by the carbothermal reduction ofaluminum oxide in the presence of gaseous nitrogen or ammonia or bydirect nitridation of aluminum. In order to get fully dense form, Y₂O₃or CaO are required as additives during the hot pressing.

Among the agriculture waste products, there are two types, onecontaining silica and carbonaceous matter and the other one containsmostly carbonaceous matter and no silica. The first kind includes ricehusk, wheat husk, and peanut shells. We have demonstrated that they canbe utilized to produce industrially important materials such as SiO₂,SiC, Si₃N₄, and zinc silicate by pyrolyzing them in air, argon or innitrogen atmospheres.

The second kind of agriculture residues are nut shells which containonly carbonaceous matter such as almond, walnuts, pistachio, coconuts,macadamia, cashew, etc. Billions of pounds of nut shells are producedannually all over the world and will be available if they can beharnessed in the synthesis of industrially important materials.Recently, it was reported that mixed phases of SiC and Si₃N₄ can beproduced by carbothermal reduction and nitridation of a mixture ofsilica and macadamia powder.

We have demonstrated in our recent work that by adding ZnO to powder ofwheat or rice husk, pure zinc silicate can be produced withphoto-luminescent properties.

Here, we have developed the formation of AlN from the nut shells powderby adding nanocrystalline powders of Al₂O₃ to the nut shells powder ofalmond, walnut, coconut, macadamia, pistachio and cashew and pyrolysingthem in nitrogen atmosphere at 1400 to 1500° C.

Energy dispersive X-ray fluorescence technique was used to determine theelemental composition of the nuts with very slight variation among them.The formation of pure wurtzite phase of AlN was confirmed by x-raydiffraction and Rietveld analysis and Raman spectroscopy. Transmissionelectron microscopy was used to confirm the nanocrystallinity of AlN andto characterize the size distribution.

SUMMARY OF DISCLOSURE Description

A new method of making Aluminum Nitride from Nut Shells involving theformation of abundant quantities of AlN from a thermal treatment of amixture of aluminum oxide (Al₂O₃) and shells of almond, cashew,coconuts, pistachio, and walnuts in a nitrogen atmosphere attemperatures in excess of 1450° C.

DESCRIPTION OF THE DRAWINGS

The following description and drawings set forth certain illustrativeimplementations of the disclosure in detail, which are indicative ofseveral exemplary ways in which the various principles of the disclosuremay be carried out. The illustrated examples, however, are notexhaustive of the many possible embodiments of the disclosure. Otherobjects, advantages and novel features of the disclosure will be setforth in the following detailed description when considered inconjunction with the drawings.

FIG. 1 illustrates X-ray diffraction patterns taken with CuKα radiationof AlN synthesized from Almond powder and aluminum oxide powder innitrogen at a temperature of 1450° C. showing the wurtzite phase.

FIG. 2A illustrates a TEM micrograph of AlN samples fabricated fromalmond showing the nanocrystalline nature.

FIG. 2B illustrates a TEM micrograph of AlN samples fabricated fromalmond showing the nanocrystalline nature.

FIG. 2C illustrates a TEM micrograph of AlN samples fabricated fromwalnut showing the nanocrystalline nature.

FIG. 2D illustrates a TEM micrograph of AlN samples fabricated fromwalnut showing the nanocrystalline nature.

FIG. 3 illustrates Raman Spectra of the AlN sample derived from almondconfirming the wurtzite phase.

FIG. 4A illustrates X-ray diffraction scan of Al₂O₃ mixed with almondshowing peaks corresponding to corundum phase. The vertical linescorrespond to the expected peaks of alumina.

FIG. 4B illustrates a Rietveld whole profile analysis of the diffractionpattern for the AlN sample derived from almond after pyrolysing in anitrogen atmosphere followed by treatment in air at 800° C.

FIG. 5A illustrates Raman spectra of AlN derived from pistachio showingthe different Raman active modes.

FIG. 5B illustrates Raman spectra of AlN derived from almond showing thedifferent Raman active modes.

FIG. 5C illustrates FTIR spectra of AlN derived from pistachio showing abroad band of 699 cm⁻¹.

FIG. 5D illustrates FTIR spectra of AlN derived from almond showing abroad band of 698 cm⁻¹.

FIG. 6 illustrates EDX of AlN derived from almond nut shell afterpyrolysing in N₂ and followed by heat treatment in O₂ to removeexcessive carbon.

DETAILED DESCRIPTION OF THE INVENTION

A method of making Aluminum Nitride Synthesis from Nut Shells.

Here, the inventors have discovered a method of forming pure AlN bycarbothermal reduction of Al₂O₃ with raw nuts of almonds, coconuts,macadamia, pistachios, and walnuts in the presence of a N₂ atmosphere toproduce nano-tubes and nanoparticles previously not formed by otherprocessing then purified in an O₂ atmosphere in a Al₂O₃ crucible.

Example 1

The production process involves preparing samples from powders of rawnuts of almonds, coconuts, macadamia, pistachios, and walnuts aftermixing them with nanocrystalline Al₂O₃ powder using ball milling with aSPEX 8000M including stainless steel milling media.

Example 2

The Al₂O₃ sample along with the specific nut shell was combined andmilled to obtain a uniform powder. A hydraulic press was used topressurize the homogenous powder into 1 cm diameter disks with a 2.5-3mm depth.

The pellets were heat treated (pyrolised) in a conventional furnace attemperatures exceeding 1400° C. for an interval of 5-6 hours in anitrogen atmosphere. In order to eliminate the residual carbon, thepellets were then placed in air at 670° C.

Example 3

XRD scans were obtained using a Rigaku 18 kW rotating anode generatorand a high resolution powder diffractometer. The diffraction scans werecollected using monochromatic CuKα radiation.

Raman spectra were collected on an in Via Raman Microscope (Renishaw)using a 514 nm laser line.

Scans were obtained at ca. 15 mW laser power at the sample and anintegration period of 30 seconds.

Fourier Transform Infrared (FTIR) spectra were collected using ThermoScientific Nicolet FT-IR spectrometer with Diffuse Reflectance InfraredTransform Spectroscopy (DRIFTS) accessory.

Example 4

In order to conduct the TEM analysis, ethyl alcohol was mixed with thepyrolyzed sample; the mixture was then set in an ultrasonic cleaner.

A carbon covered 200 mesh copper grid was submerged into the mixture tocollect AlN particles.

A FEI Tecnai G2 TEM was utilized to examine the sample at 300 kV.

Nuts have very little SiO₂ uptake from the ground but still is a carbonsource. Therefore nuts are a great candidate to mix with oxides to forma carbide and/or a nitride with further processing. The result is a purenitride (in this case AlN) that is made in a simple cost effectiveprocess.

AlN made from nuts such as almonds, pistachios, walnuts, cashew,coconuts, macadamia etc. can be made fully dense without the use ofother dopants like AlN made in other ways. This provides a more purebulk form of AlN.

Due to its unique properties, it is extremely useful for the Navy. AlNits applications have been developed mainly for aeronautics andtransport fields.

Other applications of AlN lie in refractory composites for handling ofaggressive molten metals, and high efficiency heat exchange systems.

The formation of pure AlN from nut shells offers a simple route ascompared to complicated reactions currently being used involving carbonrich agents and at elevated temperatures.

Moving to more environmentally greener processes is important. Thisprocess should become the standard processing for obtaining Pure AlN.

The above examples are merely illustrative of several possibleembodiments of various aspects of the present disclosure, whereinequivalent alterations and/or modifications will occur to others skilledin the art upon reading and understanding this specification and theannexed drawings. In addition, although a particular feature of thedisclosure may have been illustrated and/or described with respect toonly one of several implementations, such feature may be combined withone or more other features of the other implementations as may bedesired and advantageous for any given or particular application. Also,to the extent that the terms “including”, “includes”, “having”, “has”,“with”, or variants thereof are used in the detailed description and/orin the claims, such terms are intended to be inclusive in a mannersimilar to the term “comprising”.

What we claim is:
 1. A method of producing nano-structures of AluminumNitride from nut shells comprising: milling agricultural nuts into afine nut powder; milling nanocrystalline Al₂O₃ into a powder; mixing thefine nut powder with the powder of nanocrystalline Al₂O₃; pressing thefine nut powder and the powder of nanocrystalline Al₂O₃ into a pellet;providing a nitrogen atmosphere; heating the pellet to a temperature ofabout 1400° C.; maintaining the temperature of the pellet at about 1400°C.; cooling the pellet in air to a temperature of about 670° C.;eliminating the residual carbon; and forming nano-structures of AlN. 2.The method of producing nano-structures of Aluminum Nitride from nutshells of claim 1 wherein the step of maintaining the temperature of thepellet at about 1400° C. comprises an interval of 5-6 hours.
 3. Anano-structured Aluminum Nitride product from nut shells in a pure formand in the wurtzite phase from the steps comprising: millingagricultural nuts into a fine nut powder; milling nanocrystalline Al₂O₃into a powder; mixing the fine nut powder with the powder ofnanocrystalline Al₂O₃; pressing the fine nut powder and the powder ofnanocrystalline Al₂O₃ into a pellet; providing a nitrogen atmosphere;heating the pellet to a temperature of about 1400° C.; maintaining thetemperature of the pellet at about 1400° C.; cooling the pellet in airto a temperature of about 670° C.; eliminating the residual carbon; andforming nano-structures of AlN.
 4. An Aluminum Nitride (AlN) productfrom nut shells made from the steps of: preparing powders ofagricultural nuts using ball milling including stainless steel millingmedia; preparing powders of nanocrystalline Al₂O₃ using ball millingincluding stainless steel milling media; mixing the powders ofagricultural nuts and the powders of nanocrystalline Al₂O₃ using ballmilling including stainless steel milling media and thereby forming ahomogenous sample powder of agricultural nuts and Al₂O₃; pressurizingthe homogenous sample powder of agricultural nuts and Al₂O₃ into a disk;heat treating or pyrolyzing the disk in a nitrogen atmosphere; andreacting the disk and the nitrogen atmosphere and forming AlN; whereinthe AlN is nano-structured AlN and in a pure form and in the wurtzitephase of AlN.
 5. The nano-structured Aluminum Nitride product in a pureform and in the wurtzite phase of claim 4 wherein the steps furthercomprise the step of: eliminating residual carbon by placing the disk inair after the step of reacting the disk and the nitrogen atmosphere andforming AlN.
 6. The nano-structured Aluminum Nitride product in a pureform and in the wurtzite phase of claim 5 wherein the step of heattreating or pyrolyzing the disk comprises temperatures exceeding 1400°C. for an interval of 5-6 hours in a nitrogen atmosphere.
 7. Thenano-structured Aluminum Nitride product in a pure form and in thewurtzite phase of claim 4 wherein the step of eliminating the residualcarbon by placing the disk in air involves a temperature of 670° C.; andwherein the step of heat treating or pyrolyzing the disk comprises aconventional furnace.